SNVSBF4 November   2019 LDC1001-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Typical Application — Axial Distance Sensing
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Inductive Sensing
      2. 7.3.2 Measuring Parallel Resonance Impedance and Inductance With LDC1001-Q1
        1. 7.3.2.1 Measuring Inductance
          1. 7.3.2.1.1 Example
    4. 7.4 Device Functional Modes
      1. 7.4.1 INTB Pin Modes
        1. 7.4.1.1 Comparator Mode
        2. 7.4.1.2 Wake-Up Mode
        3. 7.4.1.3 DRDYB Mode
    5. 7.5 Programming
      1. 7.5.1 Digital Interface
        1. 7.5.1.1 SPI Description
        2. 7.5.1.2 Extended SPI Transactions
    6. 7.6 Register Map
      1. 7.6.1 Register Description
        1. 7.6.1.1  Revision ID (offset = 0x00) [reset = 0x80]
          1. Table 2. Revision ID Field Descriptions
        2. 7.6.1.2  Rp_MAX (offset = 0x01) [reset = 0x0E]
          1. Table 3. Rp_MAX Field Descriptions
        3. 7.6.1.3  Rp_MIN (offset = 0x02) [reset = 0x14]
          1. Table 4. Rp_MIN Field Descriptions
        4. 7.6.1.4  Sensor Frequency (offset = 0x03) [reset = 0x45]
          1. Table 5. Sensor Frequency Field Descriptions
        5. 7.6.1.5  LDC Configuration (offset = 0x04) [reset = 0x1B]
          1. Table 6. LDC Configuration Field Descriptions
        6. 7.6.1.6  Clock Configuration (offset = 0x05) [reset = 0x01]
          1. Table 7. Clock Configuration Field Descriptions
        7. 7.6.1.7  Comparator Threshold High LSB (offset = 0x06) [reset = 0xFF]
          1. Table 8. Comparator Threshold High LSB Field Descriptions
        8. 7.6.1.8  Comparator Threshold High MSB (offset = 0x07) [reset = 0xFF]
          1. Table 9. Comparator Threshold High MSB Field Descriptions
        9. 7.6.1.9  Comparator Threshold Low LSB (offset = 0x08) [reset = 0x00]
          1. Table 10. Comparator Threshold Low LSB Field Descriptions
        10. 7.6.1.10 Comparator Threshold Low MSB (offset = 0x09) [reset = 0x00]
          1. Table 11. Comparator Threshold Low MSB Field Descriptions
        11. 7.6.1.11 INTB Pin Configuration (offset = 0x0A) [reset = 0x00]
          1. Table 12. INTB Pin Configuration Field Descriptions
        12. 7.6.1.12 Power Configuration (offset = 0x0B) [reset = 0x00]
          1. Table 13. Power Configuration Field Descriptions
        13. 7.6.1.13 Status (offset = 0x20) [reset = NA]
          1. Table 14. Status Field Descriptions
        14. 7.6.1.14 Proximity Data LSB (offset = 0x21) [reset = NA]
          1. Table 15. Proximity Data LSB Field Descriptions
        15. 7.6.1.15 Proximity Data MSB (offset = 0x22) [reset = NA]
          1. Table 16. Proximity Data MSB Field Descriptions
        16. 7.6.1.16 Frequency Counter LSB (offset = 0x23) [reset = NA]
          1. Table 17. Frequency Counter LSB Field Descriptions
        17. 7.6.1.17 Frequency Counter Mid-Byte (offset = 0x24) [reset = NA]
          1. Table 18. Frequency Counter Mid-Byte Field Descriptions
        18. 7.6.1.18 Frequency Counter MSB (offset = 0x25) [reset = NA]
          1. Table 19. Frequency Counter MSB Field Descriptions
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Calculation of Rp_Min and Rp_Max
        1. 8.1.1.1 Rp_MAX
        2. 8.1.1.2 Rp_MIN
      2. 8.1.2 Output Data Rate
        1. 8.1.2.1 Example
      3. 8.1.3 Selecting a Filter Capacitor (CFA and CFB Pins)
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Sensor and Target
        2. 8.2.2.2 Calculating a Sensor Capacitor
        3. 8.2.2.3 Selecting a Filter Capacitor
        4. 8.2.2.4 Setting Rp_MIN and Rp_MAX
        5. 8.2.2.5 Calculating Minimum Sensor Frequency
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.1 Inductive Sensing

An alternating current (AC) flowing through a coil generates an AC magnetic field. If a conductive material, such as a metal target, is brought into the vicinity of the coil, this magnetic field induces circulating currents (eddy currents) on the surface of the target. These eddy currents are a function of the distance, size, and composition of the target. These eddy currents then generate a magnetic field that opposes the original field generated by the coil. This mechanism is best compared to a transformer, where the coil is the primary core and the eddy current is the secondary core. The inductive coupling between both cores depends on distance and shape. Hence the resistance and inductance of the secondary core (eddy current), shows up as a distant dependent resistive and inductive component on the primary side (coil). Figure 5 through Figure 8 show a simplified circuit model.

LDC1001-Q1 inductor_modeled_resistor_slos886.gifFigure 5. Inductor With a Metal Target

Eddy currents generated on the surface of the target can be modeled as a transformer as shown in Figure 6. The coupling between the primary and secondary coils is a function of the distance and characteristics of the conductor. In Figure 6, the inductance Ls is the inductance of the coil, and rs is the parasitic series resistance of the coil. The inductance L(d), which is a function of distance, d, is the coupled inductance of the metal target. Likewise, R(d) is the parasitic resistance of the eddy currents.

LDC1001-Q1 metal_target_eddy_currents_slos886.gifFigure 6. Metal Target Modeled as L and R With Circulating Eddy Currents

Generating an alternating magnetic field with just an inductor consumes a large amount of power. This power consumption can be reduced by adding a parallel capacitor, turning the right part of Figure 6 into a resonator as shown in Figure 7. In this manner the power consumption is reduced to the eddy and inductor losses rs + R(d) only.

LDC1001-Q1 LC_tank_oscillator_slos886.gifFigure 7. LC Tank Connected to Oscillator

The LDC1001-Q1 device does not directly measure the series resistance. Instead, the device measures the equivalent parallel resonance impedance RP (see Figure 8). This representation is equivalent to the representation shown in Figure 8, where the parallel resonance impedance RP(d) is given by Equation 1.

LDC1001-Q1 equivalent_res_parallel_LC_tank_slos886.gifFigure 8. Equivalent Resistance of rs in Parallel With LC Tank
Equation 1. RP(d) = (1 ⁄ ([rs + R(d)]) × ([Ls + L(d)]) / C
Equation 2. RP = (1 / rs) × (L / C)

Figure 9 shows the variation in RP as a function of distance for a 14-mm diameter PCB coil (23 turns, 4-mil trace width, 4-mil spacing between trace, 1-oz copper thickness, FR4). The target metal used is a stainless steel 2-mm thick.

LDC1001-Q1 tc01_Rp_vs_distance_slos886.gifFigure 9. Typical RP vs Distance With a 14-mm PCB Coil